The present invention relates generally to interface devices between humans and computers, and more particularly to computer interface devices that provide force feedback to the user.
Virtual reality computer systems provide users with the illusion that they are part of a xe2x80x9cvirtualxe2x80x9d environment. A virtual reality system will typically include a computer processor, such as a personal computer or workstation, specialized virtual reality software, and virtual reality I/O devices such as head mounted displays, sensor gloves, three dimensional (xe2x80x9c3Dxe2x80x9d) pointers, etc.
Virtual reality computer systems can be used for training. In many fields, such as aviation and vehicle and systems operation, virtual reality systems have been used successfully to allow a user to learn from and experience a realistic xe2x80x9cvirtualxe2x80x9d environment. The appeal of using virtual reality computer systems for training relates, in part, to the ability of such systems to allow trainees the luxury of confidently operating in a highly realistic environment and making mistakes without xe2x80x9creal worldxe2x80x9d consequences. For example, a virtual reality computer system can allow a doctor-trainee or other human operator or user to xe2x80x9cmanipulatexe2x80x9d a scalpel or probe within a computer-simulated xe2x80x9cbodyxe2x80x9d, and thereby perform medical procedures on a virtual patient. In this instance, the I/O device which is typically a 3D pointer, stylus, or the like is used to represent a surgical instrument such as a scalpel or probe. As the xe2x80x9cscalpelxe2x80x9d or xe2x80x9cprobexe2x80x9d moves within a provided space or structure, results of such movement are updated and displayed in a body image displayed on the screen of the computer system so that the operator can gain the experience of performing such a procedure without practicing on an actual human being or a cadaver. In other applications, virtual reality computer systems allow a user to handle and manipulate the controls of complicated and expensive vehicles and machinery for training and/or entertainment purposes. For example, a pilot or astronaut in training can operate a fighter aircraft or spacecraft by manipulating controls such as a control joystick and other buttons and view the results of controlling the aircraft on a virtual reality simulation of the aircraft in flight. In yet other applications, a user can manipulate objects and tools in the real world, such as a stylus, and view the results of the manipulation in a virtual reality world with a xe2x80x9cvirtual stylusxe2x80x9d viewed on a screen, in 3-D goggles, etc.
For virtual reality systems to provide a realistic (and therefore effective) experience for the user, sensory feedback and manual interaction should be as natural as possible. As virtual reality systems become more powerful and as the number of potential applications increases, there is a growing need for specific human/computer interface devices which allow users to interface with computer simulations with tools that realistically emulate the activities being represented within the virtual simulation. While the state of the art in virtual simulation and medical imaging provides a rich and realistic visual feedback, there is a great need for new human/computer interface tools which allow users to perform natural manual interactions with the computer simulation.
In addition to sensing and tracking a user""s manual activity and feeding such information to the controlling computer to provide a 3D visual representation to the user, a human interface mechanism should also provide force or tactile (xe2x80x9chapticxe2x80x9d) feedback to the user. The need for the user to obtain realistic tactile information and experience tactile sensation is extensive in many kinds of simulation and other applications. For example, in medical/surgical simulations, the xe2x80x9cfeelxe2x80x9d of a probe or scalpel simulator is important as the probe is moved within the simulated body. It would invaluable to a medical trainee to learn how an instrument moves within a body, how much force is required depending on the operation performed, the space available in a body to manipulate an instrument, etc. In simulations of vehicles or equipment, force feedback for controls such as a joystick can be necessary to realistically teach a user the force required to move the joystick when steering in specific situations, such as in a high acceleration environment of an aircraft. In virtual world simulations where the user can manipulate objects, force feedback is necessary to realistically simulate physical objects; for example, if a user touches a pen to a table, the user should feel the impact of the pen on the table. An effective human/computer interface not only acts as an input device for tracking motion, but also as an output device for producing realistic tactile sensations. A xe2x80x9chigh bandwidthxe2x80x9d interface system, which is an interface that accurately responds to signals having fast changes and a broad range of frequencies as well as providing such signals accurately to a control system, is therefore desirable in these and other applications.
In addition, there is a desire to provide force feedback to users of computer systems in the entertainment industry. Joysticks and other interface devices can be used to provide force feedback to a user playing a video game or experiencing a simulation for entertainment purposes. Through such an interface device, a computer system can convey to the user the physical sensation of colliding into a wall, moving through a liquid, driving over a bumpy road, and other sensations. The user can thus experience an entire sensory dimension in the gaming experience that was previously absent. Force feedback interfaces can provide a whole new modality for human-computer interaction.
There are number of devices that are commercially available for interfacing a human with a computer for virtual reality simulations. There are, for example, 2-dimensional input devices such as mice, trackballs, joysticks, and digitizing tablets. However, 2-dimensional input devices tend to be awkward and inadequate to the task of interfacing with 3-dimensional virtual reality simulations. 3-dimensional interface devices are also available. A 3-dimensional human/computer interface tool sold under the trademark Immersion PROBE(trademark) is marketed by Immersion Human Interface Corporation of Santa Clara, Calif., and allows manual control in 3-dimensional virtual reality computer environments. A pen-like stylus allows for dexterous 3-dimensional manipulation in six degrees of freedom, and the position and orientation of the stylus is communicated to a host computer. The Immersion PROBE, however, does not provide force feedback to a user and thus does not allow a user to experience an entire sensory dimension in virtual reality simulations. Prior art force feedback joysticks provide physical sensations to the user by controlling motors that are coupled to the joystick.
In typical multi-degree of freedom apparatuses that include force feedback, there are several disadvantages. Since actuators which supply force feedback tend to be heavier and larger than sensors, they would provide inertial constraints if added to a device such as the Immersion PROBE. There is also the problem of coupled actuators. In a typical force feedback device, a serial chain of links and actuators is implemented to achieve multiple degrees of freedom in a desired object positioned at the end of the chain, i.e., each actuator is coupled to the previous actuator. The user who manipulates the object must carry the inertia of all of the subsequent actuators and links except for the first actuator in the chain, which is grounded. While it is possible to ground all of the actuators in a serial chain by using a complex transmission of cables or belts, the end result is a low stiffness, high friction, high damping transmission which corrupts the bandwidth of the system, providing the user with an unresponsive and inaccurate interface. These types of interfaces also introduce tactile xe2x80x9cnoisexe2x80x9d to the user through friction and compliance in signal transmission and limit the degree of sensitivity conveyed to the user through the actuators of the device.
Other existing devices provide force feedback to a user. In U.S. Pat. No. 5,184,319, by J. Kramer, an interface is described which provides force and texture information to a user of a computer system. The interface consists of an glove or xe2x80x9cexoskeletonxe2x80x9d which is worn over the user""s appendages, such as fingers, arms, or body. Forces can be applied to the user""s appendages using tendon assemblies and actuators controlled by a computer system to simulate force and textual feedback. However, the system described by Kramer is not easily applicable to simulation environments such as those mentioned above where an object is referenced in 3D space and force feedback is applied to the object. The forces applied to the user in Kramer are with reference to the body of the user; the absolute location of the user""s appendages are not easily calculated. In addition, the exoskeleton devices of Kramer can be cumbersome or even dangerous to the user if extensive devices are worn over the user""s appendages. Furthermore, the devices disclosed in Kramer are complex mechanisms in which many actuators must be used to provide force feedback to the user.
In addition, low-cost and portable mechanical interfaces which can provide force feedback are desirable. For example, personal computers for the home consumer are becoming powerful and fast enough to provide force feedback to the typical mass market consumer. A need is thus arising to be able to manufacture and market force feedback interfaces as cheaply and as efficiently as possible. The cost, complexity, reliability, and size of a force feedback interface for home use should be practical enough to mass produce the devices. In addition, aesthetic concerns such as compactness and operating noise level of a force feedback device are of concern in the home market. Since the prior art feedback interfaces are mainly addressed to specific applications in industry, most force feedback mechanisms are costly, large, heavy, have significant power requirements, are difficult to program for applications. The prior art devices require high speed control signals from a controlling computer for stability, which usually requires more expensive and complex electronics. In addition, the prior art force feedback devices are typically large and noisy. These factors provide many obstacles to the would-be manufacturer of force-feedback interfaces to the home computer market.
Therefore, a less complex, less expensive alternative to a human/computer interface tool having force feedback, lower inertia, higher bandwidth, and less noise is desirable for certain applications.
The present invention provides a human/computer interface apparatus and method which can provide from one to six degrees of freedom to a user-manipulable object and low cost, highly realistic force feedback to the user of the apparatus. The structure of the apparatus permits transducers to be positioned such that their inertial contribution to the system is very low. A number of the members of the mechanical interface can be manufactured as a single member, providing a low cost interface for a high volume market. In addition, a friction drive mechanism and voice coil actuators provide additional low cost alternatives for the interface.
An interface apparatus and method of the present invention for interfacing the motion of a user-manipulable object with an electrical system includes a user object physically contacted by a user. A gimbal mechanism is coupled to the user object, such as a joystick or a medical tool, and provides at least two degrees of freedom to the user object, where the gimbal mechanism includes multiple members. A selected number of those members are segments formed as a unitary member which provides flex between the selected members. An actuator applies a force along a degree of freedom to the user object in response to electrical signals produced by the electrical system. A sensor detects a position of the user object along the degree of freedom and outputs sensor signals to the electrical system. The actuator and sensor thus provide an electromechanical interface between the user object and the electrical system. An actuator provides force to the user object along each degree of freedom, and the actuators are decoupled from each other.
The gimbal mechanism preferably provides at least two revolute degrees of freedom to the user object about axes of rotation. Alternatively, the gimbal mechanism can provide at least two linear degrees of freedom along linear axes. In a preferred embodiment, the multiple members of the gimbal mechanism are formed as a closed-loop linkage. The linkage can include four members that are flexibly coupled to each other as segments of the unitary member. The four members include first and second extension members and first and second flexible central members, where the central members are each coupled to an extension member and to each other at the user object. A ground member is coupled to a ground surface and is rotatably coupled to the unitary flexible member by bearings. Other embodiments include coupling an object member to the user object and to the central members, and rotating the object member in a third xe2x80x9cspinxe2x80x9d degree of freedom, where the rotation in the third degree of freedom is allowed by the flexibility of the central members. In yet other embodiments, the ends of the central members are rotatably coupled to the extension members by bearings, and the central members are flexibly coupled to the user object. In another embodiment, the ends of the central members are flexibly coupled to the extension members and the central members are rotatably coupled to the user object by a bearing. In yet another embodiment, a third central member is flexibly coupled between one of the extension members and the user object. A linear axis member can be coupled to the gimbal mechanism to provide the user object with a third linear degree of freedom. A passive damper element can also be coupled to at least one member of the gimbal mechanism to increase dynamic stability of the interface system. Finally, a capstan drive mechanism, including a cable and pully, can used to transmit forces to and from the actuator/sensor and the user with no substantial backlash.
In another preferred embodiment, the interface apparatus interfaces the motion of the user object with the electrical system, which is a host computer. The host computer system can display images to the user on a display screen. A local microprocessor, separate from the host computer and controlled by software instructions, is used to communicate with the host computer via a communication interface by receiving a host command from the host computer. The actuator applies a force to the gimbal mechanism along a degree of freedom to the user object in accordance with a processor command received from the processor. The processor command is derived from the host command. Finally, the sensor detects positions of the user object along a degree of freedom and outputs the sensor signals to the host computer system. The sensor signals include information representative of the position of the user object. Preferably, the sensor is electrically coupled to the processor and outputs the sensor signals to the processor, and the processor sends the sensor signals to the host computer. The processor provides the processor command to the actuator using a processor subroutine selected in accordance with the host command and stored in a memory device. The processor also utilizes the sensor signals to help determine a force output by the actuator. In addition, the processor preferably can use timing information from a clock coupled to the processor to determine the force output by the actuator. The communication interface can include a serial interface which, although relatively slow, may be used to provide accurate force feedback by using the local microprocessor.
In yet another preferred embodiment of an interface apparatus of the present invention, the actuators for applying forces to the user object include voice coil actuators. These actuators apply a current to a wire coil within a magnetic field to produce a force on the coil and a moveable member to which the coil is attached. The produced force has a particular direction depending on the direction of a current flowed through said coil and a magnitude depending on the magnitude of the current. Preferably, an electrical interface is electrically coupled between the voice coil actuators and the electrical system/host computer, and the electrical interface preferably includes a voice coil driver chip for driving the voice coil actuators. The voice coil driver chip preferably has a variable gain of voltage input to current output to provide more realistic and a greater range of forces. In an alternate embodiment, the wire coil includes multiple sub-coils that each include a different number of loops. Constant magnitude currents can thus be flowed through selected sub-coils to create different force values on the user object. In addition, the voice coil may includes one coil of wire to apply the force to the user object, and a second coil of wire used as a sensor for sensing a velocity of the user-manipulable object.
In one preferred voice coil actuator interface embodiment, the user object is coupled to a planar member, such as a circuit board. The circuit board is translatable in two degrees of freedom, and this translation causes the user object to move in two user object degrees of freedom. In one embodiment, the user object is coupled to a ball joint that is rotatable in a socket, such that translation of the circuit board causes the ball joint to rotate in the socket and thus causes the user object to pivot in two rotary two degrees of freedom. In another embodiment, the user object is coupled directly to the circuit board and is translated in linear degrees of freedom as the planar member is translated. The coils of wire included in the voice coil actuators can be etched onto the circuit board. In addition, the voice coil driver chips used for driving the voice coil actuators, and other electronic components, can be included on the circuit board.
In another preferred embodiment, the interface apparatus includes a friction drive mechanism coupled between an actuator and a gimbal mechanism of the interface apparatus. Force from the actuator is transmitted to the gimbal mechanism through frictional contact of members of the friction drive mechanism. The friction drive mechanism preferably includes a rotatable drum having a drive bar. A drive roller is coupled to the actuator and frictionally engages the drive bar to rotate the drum and transmit a force to the object in a degree of freedom. Preferably, one or more passive rollers are frictionally engaged with the drive bar on the opposite side of the drive bar to the drive roller, so that a greater compression force is provided between the drive roller and the drive bar. The passive rollers can be spring loaded to the drive roller to provide greater compression force. Preferably, a friction drive mechanism is provided for a second degree of freedom actuator as well. In an alternate embodiment, the friction drive mechanism includes a translatable drum having a drive bar, where the drive roller frictionally engages the drive bar to translate the drum and apply a linear force to the object in a linear degree of freedom.
The interface apparatus of the present invention includes several low cost components that are suitable for providing accurate force feedback for the home market and other markets. The flexible unitary member of the preferred gimbal mechanism can be produced as one part without incurring expenses for bearings and assembly procedures. The embodiments of the present invention including the voice coil actuators utilize readily-available, cheap components that are able to produce realistic forces for the user. The friction drive mechanism of the present invention is able to transmit forces and provide mechanical advantage using low cost parts. These improvements allow a computer system to have more complete and accurate control over a low-cost interface providing realistic force feedback.
These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following specification of the invention and a study of the several figures of the drawing.